You should think about the type of metal/material you plan to use your grinder on. Some metal may not require a high RPM, while others you will need 9000RPM+ to make a good job of it. The more demanding the tasks, the more you will need a high quality angle grinder that can reach these extremely high speeds. Another consideration that goes hand in hand with speed is horsepower.
How Well Built is it?
You should make sure you go for a good angle grinder with lots of reviews. It’s best to have a look around online forums about DIY so you can get a sense for what the community feels about a given product. I wouldn’t recommend buying a cheap crappy model as it will only cost you more down the line when you need to get it repaired etc.
Different Disc Sizes
There are a few different options when it comes to choosing the size of angle grinder you want. The choices can range from 3 inches up to about 10. This is basically only needed to worry about if you need extremely large discs for your projects (most people don’t).
Watch this video guide